The third season of the American serial dramatelevision seriesLost commenced airing in the United States and Canada on October 4, 2006 and concluded on May 23, 2007. The third season continues the stories of a group of over 40 people who have been stranded on a remote island in the South Pacific, after their airplane crashed 68 days prior to the beginning of the season. In the Lost universe, the season takes place from November 28 to December 21, 2004. The producers have stated that as the first season is about introducing the survivors and the second season is about the hatch, the third season is about the Others, a group of mysterious island inhabitants.[1]

In response to fan complaints about scheduling in the previous seasons, ABC decided to air the episodes without reruns, albeit in two separate blocks.[2] In the United States, the first block consisted of six episodes aired on Wednesdays at 9:00 pm and after a twelve-week break, the season continued with the remaining 16 episodes at 10:00 pm.[3] In addition, three clip-shows recapped previous events on the show. "Lost: A Tale of Survival" aired a week before the season premiere, "Lost Survivor Guide" aired before the seventh episode[4] and "Lost: The Answers" aired before the season finale.[5]Buena Vista Home Entertainment released the season under the title Lost: The Complete Third Season – The Unexplored Experience on December 11, 2007 in Region 1 on DVD and Blu-ray Disc.[6]

The season featured 16 major roles with star billing, making it the second largest ensemble cast of the 2006–2007 television season, behind ABC's Desperate Housewives. Characters are briefly summarized and ordered by billing and number of third season appearances.

After criticism… reached its zenith, the backlash drew a backlash. Down the stretch, critics lauded Lost for one powerhouse episode after another, satisfying frustrated viewers by providing long-sought answers to some mysteries while simultaneously igniting strong new plotlines.

The first block of episodes was criticized for raising too many mysteries[24] and not providing enough answers.[25] Complaints were also made about the limited screen-time for many of the main characters in the first block.[26] Locke, played by Terry O'Quinn, who had tied for the highest second-season episode count, appeared in only 14 of the 23 episodes in the third season – only two more than guest star M.C. Gainey, who played Tom. Reaction to two new characters, Nikki and Paulo, was generally negative, with Lindelof even acknowledging that the couple was "universally despised" by fans.[27] The decision to split the season[28] and the American timeslot switch after the hiatus were also criticized.[29] Cuse acknowledged that "No one was happy with the six-episode run."[30]

The second block of episodes was critically acclaimed however,[31] with the crew dealing with problems from the first block.[32] More answers were written into the show[33] and Nikki and Paulo were killed off.[34] It was also announced that the series would end three seasons after the third season,[35] which Cuse hoped would tell the audience that the writers knew where the story was going.[36]

The season averaged 13.74 million American viewers per episode, ranking 17th in viewership and ninth in the key adults 18–49 demographic.[43] The first block had an average close to four million more viewers than the second block,[44] with the 14th episode meeting a ratings low for the series, with 11.52 million viewers.[45] However, Lost was the most recorded program of 2007.[46]

The number in the "No. in series" column refers to the episode's number within the overall series, whereas the number in the "No. in season" column refers to the episode's number within this particular season. "Featured character(s)" refers to the character(s), whose back story is featured in the episode's flashbacks. "U.S. viewers (million)" refers to the number of viewers in the United States in millions who watched the episode as it was aired.

Jack is imprisoned in the Hydra, a Dharma Initiative station, and interrogated by an Other named Juliet. Kate and Sawyer are kept in nearby cages. Sawyer tries to escape with a teenaged Other named Karl, but they are caught. "Henry Gale", whose real name is Ben, is revealed to be the leader of the Others. In flashbacks, Jack obsessively tries to find out who his wife Sarah is having an affair with during his divorce settlement. Jack suspects his father and attacks him at an Alcoholics Anonymous meeting. Jack is arrested and bailed out by his wife.

Ben offers to take Jack off the island if he cooperates. Kate and Sawyer are let out to smash rocks and it is revealed that they are under video surveillance by Ben. On the sailboat, Sun, Jin and Sayid are ambushed by the Others. Sun shoots the Other Colleen and the boat is taken by the Others. Sun, Jin and Sayid make their way back to the survivors' camp. Flashbacks show Sun's father finding out about Sun's affair with Jae Lee. He orders Jin to kill Jae, but Jin threatens Jae instead, and Jae subsequently commits suicide.

Colleen dies and her husband Danny takes out his anger by beating Sawyer. Sawyer is deceived into thinking that a pacemaker has been implanted in him and his heart will explode if his heart rate exceeds 140 bpm. Ben reveals to Sawyer that trying to escape is futile because they are on a separate island off the coast of the island where the survivors' camp is. In flashbacks, Sawyer cons his way out of prison and finds out that he has a daughter. After claiming that he doesn't care about her, he anonymously gives a large sum of money to his daughter.

Eko follows what appears to be his brother into the jungle. It turns out to be the smoke monster, which proceeds to kill Eko. Jack finds out that the reason he was captured was to operate on Ben's spinal tumor. Juliet conspires with Jack against Ben, telling him to kill Ben during surgery but to make it look like an accident. In flashbacks, Eko becomes a priest after Yemi is killed and Eko kills a few men to protect his town.

Kate and Sawyer have sex. Danny almost kills Sawyer. Jack stops Ben's surgery and threatens to kill Ben unless Kate and Sawyer are given time to escape. In flashbacks, Kate tries to have an ordinary life and get married, but ends up running away after confessing to her husband about her past.

The teenaged Other Alex supplies Kate and Sawyer with a catamaran to return to their island, but first convinces them to help her rescue her boyfriend Karl from a room where he is being brainwashed by being forced to watch a video. Juliet kills Pickett, who is in pursuit of Kate and Sawyer. Jack finishes Ben's surgery. Flashbacks reveal that over three years prior to the crash, Juliet is a fertility doctor, and is able to make her sister fertile. Juliet is interviewed by Mittelos Bioscience.

Charlie and Hurley attempt to get Desmond drunk so he will explain to them how he is able to see the future. An extended flashback reveals what happened to Desmond after the implosion of the hatch. Desmond relives a day of his life with Penny before coming to the island. He finds himself on the island again with the ability to see flashes of the future, most notably Charlie's approaching death.

Juliet is put on trial for killing Danny. With Jack and Ben's help, Juliet does not receive the death penalty. The Others and Jack begin their journey to the Others' homes, which are located on a different island. Flashbacks show Jack getting his tattoos during a strange vacation in Thailand.

Kate and Sawyer return to the beach. Sayid and Locke follow Kate into the jungle as she seeks out Rousseau, teasing her with information about Alex. Hurley finds an old, abandoned van in the jungle, and believing this will boost spirits and give people hope, he enlists Jin, Charlie, and Sawyer to help him fix it. Flashbacks depict familial conflict when Hurley's father returns home on the heels of Hurley winning the lottery.

Locke, Sayid and Kate investigate a Dharma communications station in the jungle and meet its inhabitant, Mikhail. As they are leaving the station, Locke blows it up. Sawyer competes in a ping-pong competition against Hurley to get back his belongings, but loses and has to go without calling people nicknames for a week. In flashbacks, Sayid meets one of his former torture victims in Paris.

Claire attempts to tie a rescue message to a flock of birds, which she recognizes as being part of a scientific study. Curious and angry over Desmond and Charlie's repeated attempts to halt her project, she confronts Desmond, and he reveals his visions of Charlie's death. In flashbacks, it is revealed that Christian Shepherd is Claire's biological father, a fact she was unaware of until after a car accident put her mother in a vegetative state. On the other side of the island, Locke, Sayid, Kate, and Danielle approach a sonic barrier fence protecting the home of the Others. Locke pushes their hostage, Mikhail, through the fence, killing him instantly. The group figures out a way to climb over the fence unharmed. The final shot shows Jack playing football with Tom in the Others' encampment.

Locke, Sayid, and Kate encounter the Others' homes for the first time and find Jack relatively happy amongst them. Jack and Juliet, whose relationship has advanced, have cut a deal with Ben to leave the island on the Others' submarine, but Locke blows it up. Ben reveals that he has Locke's father in captivity. In flashbacks, Locke's father pushes him out of a window, which paralyzes Locke.

Charlie tells Sun that he and Sawyer were behind her kidnapping attempt in the jungle. The survivors investigate the apparent deaths of Nikki and Paulo. Flashbacks feature past characters such as Shannon and Boone, and show Nikki and Paulo arguing over diamonds that they conned from a millionaire television executive. On the island, Nikki releases venomous spiders upon Paulo, but they are both bitten and stuck in an eight-hour paralysis. The survivors do not figure out that Nikki and Paulo are not dead, only paralyzed, and accidentally bury them alive.

The Others and Locke leave the Others' homes, leaving behind Jack, Kate, Sayid and Juliet. It is shown the Others' sonic barrier fences stop the smoke monster from going past them. Hurley cons Sawyer into making amends with his fellow castaways. Flashbacks show the steps Kate took to reunite with her mother, who did not want her.

Jack, Sayid, Kate, and Juliet return from the Others' camp and because of his insistence that they trust Juliet, the rest of the survivors question the motives of Jack. A mysterious illness strikes Claire, activated by an implant from the Others inside her and Juliet cares for her. Flashbacks show Juliet's time on the island, kept there against her will and unable to save women who get pregnant on the island from death. Flashbacks also show Juliet conspiring with Ben to be a mole in the survivors' camp.

Led by flashes, Desmond coaxes Charlie, Hurley and Jin on a trek across the jungle where they discover Naomi, a parachutist. Kate turns to Sawyer after seeing Jack alone with Juliet. Flashbacks show Desmond's time as a monk and his meeting with Penny.

After learning that the Others' pregnant women died before giving birth on the island, Sun allows Juliet to examine her in the Dharma medical station. Juliet reports back to Ben. Desmond meets a living Mikhail in the jungle and allows him to help save the life of Naomi. Flashbacks show Sun being blackmailed by Jin's biological mother, whom Sun thought to be dead. Hurley learns from Naomi that Oceanic flight 815 was "found" with "no survivors".

Flashbacks show Locke living with the Others, who have his father in captivity. In the present, Locke persuades Sawyer to go with him to the Black Rock to see Locke's father. Sawyer kills Locke's father, who happens to be the original Sawyer.

Locke returns to the Others and Ben begrudgingly takes Locke to meet the Others' mysterious leader Jacob. Locke is unable to see Jacob, but can hear him, and because of this Ben shoots Locke and leaves him for dead. The survivors' mistrust of Jack peaks when Juliet is exposed as a mole; however, Juliet in turn reveals that she has been working with Jack against the Others. Flashbacks show when Ben first came to the island as a boy as part of the Dharma Initiative. Ben conspires with the Others (at least one of whom, Richard Alpert, does not age in the next thirty years) and kills most of Dharma.

Jack learns of the Others' plan to ambush the survivors and kidnap their pregnant women, and he comes up with a plan to kill the Others with dynamite. Desmond informs Charlie of another flash in which Claire and Aaron are saved as a result of Charlie swimming to an underwater Dharma station that is jamming all transmissions. In order for this to work, however, Charlie must die. Charlie understands his fate and successfully makes it possible for Sayid to send out a distress signal from Naomi's satellite phone. Charlie writes down the five greatest moments of his life and gives them to Desmond to give to Claire.

In this double-length episode, Jack's plan to kill the Others backfires, and Sayid, Jin, and Bernard are held hostage by the Others at the beach. Led by Rousseau, the castaways travel to the radio tower to turn off Rousseau's transmission. Naomi makes contact with her boat, but is stabbed by Locke, who along with Ben, believes that the survivors are making a mistake. After successfully shutting down the jammer, Charlie makes contact with Penny Widmore in the underwater Dharma station and discovers that Naomi's boat has nothing to do with Penny, but Charlie drowns in the communications room when Mikhail detonates a hand grenade outside the porthole. Before drowning, Charlie warns Desmond by writing on his hand, "Not Penny's Boat." Sawyer, Juliet, and Hurley rescue the castaways at the beach. Instead of flashbacks, flashforwards show Jack's miserable life after rescue from the island, culminating in a meeting with Kate in which Jack says that they weren't supposed to leave and must go back to the island.